In recent years, the cost of lumber has increased dramatically as the result of limitations placed upon the harvesting of trees in order to preserve the environment. Within the few years alone, the cost of lumber has more than doubled. This cost increase has had a major impact on the cost of new residential construction, making new homes more difficult to build and sell at affordable prices. This, in turn has resulted in the decrease in new housing starts and increased unemployment within the construction industry.
In addition to the increased expenses resulting from the high cost of lumber, there are other reasons that make it desirable to identify a viable alternative to wood for significant portions of the support structure in new construction. These reasons a related to the vulnerability of wood to insect damage and decay, and to the weight of the wood.
Pre-fabricated roof and floor trusses, and frame segments are well known in the residential and light commercial construction industries. The trusses are most commonly formed from two-by-four studs joined together by steel gussets, while the frame segments are often nailed together. The pre-fabricated roof trusses are lifted onto and attached to the top of a structural frame so that the roofing material can be placed on it. The pre-fabricated floor trusses are attached to the foundation or the lower portion of the structural frame so that plywood and flooring can be placed on top and attached thereto. The pre-fabricated components of a structure provide substantial time savings in the construction process, which can be critical when the climate in some areas permits only limited time windows suitable for construction. In general, the time savings result in cost savings. Nonetheless, the significant increase in the cost of lumber had made even these pre-fab trusses and frames so expensive that an alternative is being sought.
A lightweight steel beam has been developed by Navon which is described in PCT Application Publication Number WO 9117328, based upon U.S. patent application Ser. Nos. 07/518,554 (filed May 3, 1990) and 07/674,549 (filed Mar. 22, 1991). This structural beam is an I-beam of four piece construction, where the two bearing portions (top and bottom) have a "C"-shape and the web and flange portion consists of two pieces of sheet steel which are welded at their centers and bent outward to form the triangular flanges. This beam is illustrated in cross-section in FIG. 1, labeled "PRIOR ART". The flanges of the triangles are then welded to the insides of the "C"-shaped bearing portions to create the I-beam. Two beams are joined together by flat or angled gussets which are bolted or welded to the outer surface of the web.
While the Navon beam provides an improvement upon conventional steel beams since it is over 50% lighter and it is relatively easy to use in erecting a structure, it is not trivial to fabricate. Each beam consists of four pieces which must be bent and welded together over the entire length of the beam, making the production process one that requires several specialized pieces of machinery and consumes time. Further, the joints between two beams may be subject to excessive lateral stresses since the gussets merely attach to the outside of the web, without providing any reinforcement of the joint by the beams themselves.